1. Field of the Invention
The present invention relates to wide-angle lenses and image pickup apparatuses, and specifically to a wide-angle lens that corrects chromatic aberration with a cemented lens.
2. Description of the Related Art
Monitoring cameras and onboard cameras, in which an image forming lens is combined with an area sensor, are put into practical use. The image forming lens used in monitoring cameras, onboard cameras, etc., is preferably capable of picking up images in a wide image pickup range and required to have a wide viewing angle. Further, monitoring cameras and onboard cameras are frequently used out of doors, and brightness in image pickup environments greatly differs between the daytime and the nighttime. Therefore, the image forming lens is required to have high brightness so as to be capable of picking up images satisfactorily even at the nighttime.
Moreover, it is important that the image forming lens be small in order to meet demands for the miniaturization of monitoring cameras and onboard cameras.
As a wide-angle lens that corrects chromatic aberration with a cemented lens to obtain high resolution, Patent Document 1, for example, has disclosed one that has a viewing angle of more than 130° and an F-number of 2.8 as its brightness index.
However, when an image pickup apparatus with such a conventional wide-angle lens having an F-number of 2.8 is used, brightness in the image picked up in dark environments such as the nighttime is low, which in turn easily limits the usage of the image pickup apparatus.
Patent Document 1: JP-A-2006-284620